Numerous undercutters have been developed by the engineers of the assignee of this application and by others, each stage of undercutter development has brought improvement in speed and efficiency and has often enhanced the general purpose utility of the undercutter art. Nonetheless certain sections of track have remained inaccessible to known undercutter technology. Undercutters are often used in conjunction with large ditcher wheels which dig a trench alongside the track to permit the undercutter to reach under the track Other undercutters utilize a continuous chain which forms a loop extending beneath the track with an entry on one side and an exit on the other side of the track and continuing above the carriage upon which the drive mechanism is supported. Still other undercutters employ dual sided undercutter members, each of which remove a portion of the ballast to each side of the track. While each of these various types of undercutters are suitable for some tracks, they are unsuited for the particular track environment for which the present invention is designed. In metropolitan areas and in Europe, a great deal of commuter railroad track is located underground. Oftentimes the clearance both laterally and horizontally alongside such tracks is insufficient to permit the use of ditcher wheels or apparatus which must have access to ballast on both sides of the track. Accordingly, neither the continuous loop nor dual sided undercutters can be employed to remove ballast beneath these tracks. A similar problem exists at railroad switches where two sets of track merge or diverge. In this instance, neither the dual sided nor continuous loop undercutter can conveniently be employed.